60#include <forward_list>
66#define LLE_OPTION "loop-load-elim"
67#define DEBUG_TYPE LLE_OPTION
70 "runtime-check-per-loop-load-elim",
cl::Hidden,
71 cl::desc(
"Max number of memchecks allowed per eliminated load on average"),
76 cl::desc(
"The maximum number of SCEV checks allowed for Loop "
79STATISTIC(NumLoopLoadEliminted,
"Number of loads eliminated by LLE");
84struct StoreToLoadForwardingCandidate {
89 : Load(Load), Store(Store) {}
96 Value *LoadPtr =
Load->getPointerOperand();
99 auto &
DL =
Load->getParent()->getModule()->getDataLayout();
103 DL.getTypeSizeInBits(LoadType) ==
105 "Should be a known dependence");
107 int64_t StrideLoad =
getPtrStride(PSE, LoadType, LoadPtr, L).value_or(0);
108 int64_t StrideStore =
getPtrStride(PSE, LoadType, StorePtr, L).value_or(0);
109 if (!StrideLoad || !StrideStore || StrideLoad != StrideStore)
119 if (std::abs(StrideLoad) != 1)
122 unsigned TypeByteSize =
DL.getTypeAllocSize(
const_cast<Type *
>(LoadType));
124 auto *LoadPtrSCEV = cast<SCEVAddRecExpr>(PSE.
getSCEV(LoadPtr));
125 auto *StorePtrSCEV = cast<SCEVAddRecExpr>(PSE.
getSCEV(StorePtr));
129 auto *Dist = cast<SCEVConstant>(
131 const APInt &Val = Dist->getAPInt();
132 return Val == TypeByteSize * StrideLoad;
135 Value *getLoadPtr()
const {
return Load->getPointerOperand(); }
139 const StoreToLoadForwardingCandidate &Cand) {
140 OS << *Cand.Store <<
" -->\n";
154 L->getLoopLatches(Latches);
162 return Load->getParent() != L->getHeader();
168class LoadEliminationForLoop {
173 :
L(
L), LI(LI), LAI(LAI), DT(DT),
BFI(
BFI), PSI(PSI), PSE(LAI.getPSE()) {}
180 std::forward_list<StoreToLoadForwardingCandidate>
182 std::forward_list<StoreToLoadForwardingCandidate> Candidates;
194 for (
const auto &Dep : *Deps) {
196 Instruction *Destination = Dep.getDestination(LAI);
200 if (isa<LoadInst>(Source))
201 LoadsWithUnknownDepedence.
insert(Source);
202 if (isa<LoadInst>(Destination))
203 LoadsWithUnknownDepedence.
insert(Destination);
207 if (Dep.isBackward())
213 assert(Dep.isForward() &&
"Needs to be a forward dependence");
215 auto *
Store = dyn_cast<StoreInst>(Source);
218 auto *
Load = dyn_cast<LoadInst>(Destination);
225 Store->getParent()->getModule()->getDataLayout()))
228 Candidates.emplace_front(Load, Store);
231 if (!LoadsWithUnknownDepedence.
empty())
232 Candidates.remove_if([&](
const StoreToLoadForwardingCandidate &
C) {
233 return LoadsWithUnknownDepedence.
count(
C.Load);
241 auto I = InstOrder.find(Inst);
242 assert(
I != InstOrder.end() &&
"No index for instruction");
265 void removeDependencesFromMultipleStores(
266 std::forward_list<StoreToLoadForwardingCandidate> &Candidates) {
269 using LoadToSingleCandT =
271 LoadToSingleCandT LoadToSingleCand;
273 for (
const auto &Cand : Candidates) {
275 LoadToSingleCandT::iterator Iter;
277 std::tie(Iter, NewElt) =
278 LoadToSingleCand.
insert(std::make_pair(Cand.Load, &Cand));
280 const StoreToLoadForwardingCandidate *&OtherCand = Iter->second;
282 if (OtherCand ==
nullptr)
288 if (Cand.Store->getParent() == OtherCand->Store->getParent() &&
289 Cand.isDependenceDistanceOfOne(PSE, L) &&
290 OtherCand->isDependenceDistanceOfOne(PSE, L)) {
292 if (getInstrIndex(OtherCand->Store) < getInstrIndex(Cand.Store))
299 Candidates.remove_if([&](
const StoreToLoadForwardingCandidate &Cand) {
300 if (LoadToSingleCand[Cand.Load] != &Cand) {
302 dbgs() <<
"Removing from candidates: \n"
304 <<
" The load may have multiple stores forwarding to "
317 bool needsChecking(
unsigned PtrIdx1,
unsigned PtrIdx2,
324 return ((PtrsWrittenOnFwdingPath.
count(Ptr1) && CandLoadPtrs.
count(Ptr2)) ||
325 (PtrsWrittenOnFwdingPath.
count(Ptr2) && CandLoadPtrs.
count(Ptr1)));
352 std::max_element(Candidates.
begin(), Candidates.
end(),
353 [&](
const StoreToLoadForwardingCandidate &
A,
354 const StoreToLoadForwardingCandidate &
B) {
355 return getInstrIndex(A.Load) < getInstrIndex(B.Load);
359 std::min_element(Candidates.
begin(), Candidates.
end(),
360 [&](
const StoreToLoadForwardingCandidate &
A,
361 const StoreToLoadForwardingCandidate &
B) {
362 return getInstrIndex(A.Store) <
363 getInstrIndex(B.Store);
373 if (
auto *S = dyn_cast<StoreInst>(
I))
374 PtrsWrittenOnFwdingPath.
insert(S->getPointerOperand());
377 std::for_each(MemInstrs.begin() + getInstrIndex(FirstStore) + 1,
378 MemInstrs.end(), InsertStorePtr);
379 std::for_each(MemInstrs.begin(), &MemInstrs[getInstrIndex(LastLoad)],
382 return PtrsWrittenOnFwdingPath;
391 findPointersWrittenOnForwardingPath(Candidates);
395 for (
const auto &Candidate : Candidates)
396 CandLoadPtrs.
insert(Candidate.getLoadPtr());
401 copy_if(AllChecks, std::back_inserter(Checks),
403 for (
auto PtrIdx1 :
Check.first->Members)
404 for (
auto PtrIdx2 :
Check.second->Members)
405 if (needsChecking(PtrIdx1, PtrIdx2, PtrsWrittenOnFwdingPath,
420 propagateStoredValueToLoadUsers(
const StoreToLoadForwardingCandidate &Cand,
437 Value *
Ptr = Cand.Load->getPointerOperand();
438 auto *PtrSCEV = cast<SCEVAddRecExpr>(PSE.
getSCEV(
Ptr));
439 auto *PH =
L->getLoopPreheader();
440 assert(PH &&
"Preheader should exist!");
441 Value *InitialPtr =
SEE.expandCodeFor(PtrSCEV->getStart(),
Ptr->getType(),
442 PH->getTerminator());
444 Cand.Load->getType(), InitialPtr,
"load_initial",
445 false, Cand.Load->getAlign(), PH->getTerminator());
448 PHI->insertBefore(
L->getHeader()->begin());
449 PHI->addIncoming(Initial, PH);
452 Type *StoreType = Cand.Store->getValueOperand()->getType();
456 assert(
DL.getTypeSizeInBits(LoadType) ==
DL.getTypeSizeInBits(StoreType) &&
457 "The type sizes should match!");
459 Value *StoreValue = Cand.Store->getValueOperand();
460 if (LoadType != StoreType)
462 StoreValue, LoadType,
"store_forward_cast", Cand.Store);
464 PHI->addIncoming(StoreValue,
L->getLoopLatch());
466 Cand.Load->replaceAllUsesWith(
PHI);
472 LLVM_DEBUG(
dbgs() <<
"\nIn \"" <<
L->getHeader()->getParent()->getName()
473 <<
"\" checking " << *L <<
"\n");
494 auto StoreToLoadDependences = findStoreToLoadDependences(LAI);
495 if (StoreToLoadDependences.empty())
504 removeDependencesFromMultipleStores(StoreToLoadDependences);
505 if (StoreToLoadDependences.empty())
510 for (
const StoreToLoadForwardingCandidate &Cand : StoreToLoadDependences) {
526 if (!Cand.isDependenceDistanceOfOne(PSE, L))
529 assert(isa<SCEVAddRecExpr>(PSE.
getSCEV(Cand.Load->getPointerOperand())) &&
530 "Loading from something other than indvar?");
532 isa<SCEVAddRecExpr>(PSE.
getSCEV(Cand.Store->getPointerOperand())) &&
533 "Storing to something other than indvar?");
539 <<
". Valid store-to-load forwarding across the loop backedge\n");
541 if (Candidates.
empty())
560 if (!
L->isLoopSimplifyForm()) {
568 "convergent calls\n");
572 auto *HeaderBB =
L->getHeader();
573 auto *
F = HeaderBB->getParent();
574 bool OptForSize =
F->hasOptSize() ||
576 PGSOQueryType::IRPass);
579 dbgs() <<
"Versioning is needed but not allowed when optimizing "
592 auto NoLongerGoodCandidate = [
this](
593 const StoreToLoadForwardingCandidate &Cand) {
594 return !isa<SCEVAddRecExpr>(
595 PSE.
getSCEV(Cand.Load->getPointerOperand())) ||
596 !isa<SCEVAddRecExpr>(
597 PSE.
getSCEV(Cand.Store->getPointerOperand()));
606 for (
const auto &Cand : Candidates)
607 propagateStoredValueToLoadUsers(Cand,
SEE);
608 NumLoopLoadEliminted += Candidates.size();
644 bool Changed =
false;
646 for (
Loop *TopLevelLoop : LI)
648 Changed |=
simplifyLoop(L, &DT, &LI, SE, AC,
nullptr,
false);
650 if (L->isInnermost())
655 for (
Loop *L : Worklist) {
657 if (!L->isRotatedForm() || !L->getExitingBlock())
660 LoadEliminationForLoop LEL(L, &LI, LAIs.
getInfo(*L), &DT, BFI, PSI);
661 Changed |= LEL.processLoop();
680 auto *BFI = (PSI && PSI->hasProfileSummary()) ?
for(const MachineOperand &MO :llvm::drop_begin(OldMI.operands(), Desc.getNumOperands()))
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
This file implements a class to represent arbitrary precision integral constant values and operations...
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
static GCRegistry::Add< ErlangGC > A("erlang", "erlang-compatible garbage collector")
This file defines the DenseMap class.
This file builds on the ADT/GraphTraits.h file to build generic depth first graph iterator.
This is the interface for a simple mod/ref and alias analysis over globals.
This header provides classes for managing per-loop analyses.
static bool eliminateLoadsAcrossLoops(Function &F, LoopInfo &LI, DominatorTree &DT, BlockFrequencyInfo *BFI, ProfileSummaryInfo *PSI, ScalarEvolution *SE, AssumptionCache *AC, LoopAccessInfoManager &LAIs)
static cl::opt< unsigned > LoadElimSCEVCheckThreshold("loop-load-elimination-scev-check-threshold", cl::init(8), cl::Hidden, cl::desc("The maximum number of SCEV checks allowed for Loop " "Load Elimination"))
static bool isLoadConditional(LoadInst *Load, Loop *L)
Return true if the load is not executed on all paths in the loop.
static bool doesStoreDominatesAllLatches(BasicBlock *StoreBlock, Loop *L, DominatorTree *DT)
Check if the store dominates all latches, so as long as there is no intervening store this value will...
static cl::opt< unsigned > CheckPerElim("runtime-check-per-loop-load-elim", cl::Hidden, cl::desc("Max number of memchecks allowed per eliminated load on average"), cl::init(1))
This header defines the LoopLoadEliminationPass object.
Module.h This file contains the declarations for the Module class.
This header defines various interfaces for pass management in LLVM.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This file defines the SmallPtrSet class.
This file defines the SmallVector class.
This file defines the 'Statistic' class, which is designed to be an easy way to expose various metric...
#define STATISTIC(VARNAME, DESC)
Class for arbitrary precision integers.
A container for analyses that lazily runs them and caches their results.
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
A function analysis which provides an AssumptionCache.
A cache of @llvm.assume calls within a function.
LLVM Basic Block Representation.
Analysis pass which computes BlockFrequencyInfo.
BlockFrequencyInfo pass uses BlockFrequencyInfoImpl implementation to estimate IR basic block frequen...
static CastInst * CreateBitOrPointerCast(Value *S, Type *Ty, const Twine &Name="", Instruction *InsertBefore=nullptr)
Create a BitCast, a PtrToInt, or an IntToPTr cast instruction.
static bool isBitOrNoopPointerCastable(Type *SrcTy, Type *DestTy, const DataLayout &DL)
Check whether a bitcast, inttoptr, or ptrtoint cast between these types is valid and a no-op.
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Analysis pass which computes a DominatorTree.
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
bool dominates(const BasicBlock *BB, const Use &U) const
Return true if the (end of the) basic block BB dominates the use U.
An instruction for reading from memory.
This analysis provides dependence information for the memory accesses of a loop.
const LoopAccessInfo & getInfo(Loop &L)
Drive the analysis of memory accesses in the loop.
const MemoryDepChecker & getDepChecker() const
the Memory Dependence Checker which can determine the loop-independent and loop-carried dependences b...
const RuntimePointerChecking * getRuntimePointerChecking() const
const PredicatedScalarEvolution & getPSE() const
Used to add runtime SCEV checks.
bool hasConvergentOp() const
Return true if there is a convergent operation in the loop.
Analysis pass that exposes the LoopInfo for a function.
This class emits a version of the loop where run-time checks ensure that may-alias pointers can't ove...
Represents a single loop in the control flow graph.
const MachineFunction * getParent() const
Return the MachineFunction containing this basic block.
const DataLayout & getDataLayout() const
Return the DataLayout attached to the Module associated to this MF.
const SmallVectorImpl< Instruction * > & getMemoryInstructions() const
The vector of memory access instructions.
const SmallVectorImpl< Dependence > * getDependences() const
Returns the memory dependences.
DenseMap< Instruction *, unsigned > generateInstructionOrderMap() const
Generate a mapping between the memory instructions and their indices according to program order.
An analysis over an "inner" IR unit that provides access to an analysis manager over a "outer" IR uni...
static PHINode * Create(Type *Ty, unsigned NumReservedValues, const Twine &NameStr="", Instruction *InsertBefore=nullptr)
Constructors - NumReservedValues is a hint for the number of incoming edges that this phi node will h...
An interface layer with SCEV used to manage how we see SCEV expressions for values in the context of ...
ScalarEvolution * getSE() const
Returns the ScalarEvolution analysis used.
const SCEVPredicate & getPredicate() const
const SCEV * getSCEV(Value *V)
Returns the SCEV expression of V, in the context of the current SCEV predicate.
A set of analyses that are preserved following a run of a transformation pass.
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
void preserve()
Mark an analysis as preserved.
An analysis pass based on the new PM to deliver ProfileSummaryInfo.
Analysis providing profile information.
void printChecks(raw_ostream &OS, const SmallVectorImpl< RuntimePointerCheck > &Checks, unsigned Depth=0) const
Print Checks.
const SmallVectorImpl< RuntimePointerCheck > & getChecks() const
Returns the checks that generateChecks created.
const PointerInfo & getPointerInfo(unsigned PtrIdx) const
Return PointerInfo for pointer at index PtrIdx.
This class uses information about analyze scalars to rewrite expressions in canonical form.
virtual unsigned getComplexity() const
Returns the estimated complexity of this predicate.
virtual bool isAlwaysTrue() const =0
Returns true if the predicate is always true.
Analysis pass that exposes the ScalarEvolution for a function.
The main scalar evolution driver.
const SCEV * getMinusSCEV(const SCEV *LHS, const SCEV *RHS, SCEV::NoWrapFlags Flags=SCEV::FlagAnyWrap, unsigned Depth=0)
Return LHS-RHS.
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
void push_back(const T &Elt)
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
An instruction for storing to memory.
The instances of the Type class are immutable: once they are created, they are never changed.
unsigned getPointerAddressSpace() const
Get the address space of this pointer or pointer vector type.
LLVM Value Representation.
Type * getType() const
All values are typed, get the type of this value.
This class implements an extremely fast bulk output stream that can only output to a stream.
raw_ostream & indent(unsigned NumSpaces)
indent - Insert 'NumSpaces' spaces.
@ C
The default llvm calling convention, compatible with C.
initializer< Ty > init(const Ty &Val)
This is an optimization pass for GlobalISel generic memory operations.
bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE, AssumptionCache *AC, MemorySSAUpdater *MSSAU, bool PreserveLCSSA)
Simplify each loop in a loop nest recursively.
bool all_of(R &&range, UnaryPredicate P)
Provide wrappers to std::all_of which take ranges instead of having to pass begin/end explicitly.
std::pair< const RuntimeCheckingPtrGroup *, const RuntimeCheckingPtrGroup * > RuntimePointerCheck
A memcheck which made up of a pair of grouped pointers.
bool shouldOptimizeForSize(const MachineFunction *MF, ProfileSummaryInfo *PSI, const MachineBlockFrequencyInfo *BFI, PGSOQueryType QueryType=PGSOQueryType::Other)
Returns true if machine function MF is suggested to be size-optimized based on the profile.
OutputIt copy_if(R &&Range, OutputIt Out, UnaryPredicate P)
Provide wrappers to std::copy_if which take ranges instead of having to pass begin/end explicitly.
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
std::optional< int64_t > getPtrStride(PredicatedScalarEvolution &PSE, Type *AccessTy, Value *Ptr, const Loop *Lp, const DenseMap< Value *, const SCEV * > &StridesMap=DenseMap< Value *, const SCEV * >(), bool Assume=false, bool ShouldCheckWrap=true)
If the pointer has a constant stride return it in units of the access type size.
raw_ostream & operator<<(raw_ostream &OS, const APFixedPoint &FX)
void erase_if(Container &C, UnaryPredicate P)
Provide a container algorithm similar to C++ Library Fundamentals v2's erase_if which is equivalent t...
iterator_range< df_iterator< T > > depth_first(const T &G)
Type * getLoadStoreType(Value *I)
A helper function that returns the type of a load or store instruction.
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
TrackingVH< Value > PointerValue
Holds the pointer value that we need to check.